Stretch films are typically used in applications where it is desirable to securely hold and/or wrap an article or a group of articles, such as load palletization. The film is typically stretched tightly around the goods or plurality of articles situated on a pallet, and self-sealed while the film is still in the stretched condition to create a secure package. A limiting performance factor for stretch film is the amount the film can be stretched or elongated as it is being used to secure the package before it either breaks, tears, or begins to lose performance in other key property areas. Thus, it would be desirable to shift the onset of strain hardening to higher strains without sacrificing other important properties.
Stretch films comprising LLDPE and polypropylenes have been disclosed in US 2006/0159943, but lack desirable elasticity and strain hardening improvements over LLDPE alone. The film compositions described in WO 2007/044544 disclose LLDPE blends with propylene-based copolymers. The present invention uses the combination of propylene-based elastomers having excellent elongation and toughness properties to improve the performance of LLDPE resins commonly used in stretch films. The inventive films have delayed onset of strain hardening (higher stretch capability) and/or improved toughness that provides superior performance. Films may be blown and/or cast, monolayer blends and/or co-extrusions. The LLDPE may be conventional Ziegler-Natta LLDPEs or single site catalyzed LLDPEs.
Other disclosures of interest include US 2004/0048019A1, US 2006/0281868, US 2007/0260016, US 2007/0054997A1, U.S. Pat. No. 6,423,420 and U.S. Pat. No. 7,220,801.